This application is the US nation phase of PCT application PCT/EP99/01946 filed Mar. 1999 with a claim to the priority of German patent application 19814212.9 itself filed Mar. 31, 1998 German application 19825156.4 itself filed Jun. 5, 1998.
The invention relates to a device for applying a coating substance, comprised of a liquid resin and a fine-grained abrasive material, especially corundum, to a continuous paper web for use in the production of wear-resistant laminates.
DE 95 08 797 C1 describes a process for producing decorative paper for use in the production of wear-resistant laminates. For this purpose, a viscous mixture of melamine resin and alpha cellulose to which corundum particles have been added is deposited as a coating substance on the visible surface of a decorative paper.
The alpha cellulose serves, therefore, as a stiffening and suspending agent. The corundum particles have a grain size of 15 to 50 xcexcm. The coating quantity amounts to 80 to 200 g/m2 so that, after attaining the final moisture content, the layer thickness is 20 to 60 xcexcm. The coating substance should be applied by means of a wire doctor element, a reverse coating system or a screen roller.
It has been found in practice that any moving parts of such coating substance which come into contact with the coating substance are worn out in very brief periods of time by the abrasive corundum.
In the submission of H. Peters which appeared in the journal xe2x80x9cWeakly for paper fabricationxe2x80x9d, 6, 1973, p. 164 to 169, a nozzle coating system, inter alia, has been briefly described. In that system, a slit nozzle is trained from below on a lower region of a continuous cardboard web which is looped around a rotating roller in a hairpin shape. Downstream of the nozzle, in the movement direction, a doctor blade is arranged to smooth out the applied layer and for removal of surplus coating substance. From this publication one learns that the coating device is suitable for coating quantities up to 25 to 30 g/m2 and is especially advantageous at high speeds.
It is the object of the invention to provide a device for applying a coating substance comprised of liquid resin and fine-grained abrasive material, especially corundum, to a continuous paper web which satisfies the following requirements:
On the one hand, the coating substance should be applicable in a relatively thick uniform layer as is required for papers which are intended for the production of abrasion-resistant laminates, especially with a coating quantity of 80 to 200 g/m2.
On the other hand, the device should largely avoid the need for expensive machine components which are subject to excessive wear by the abrasive particle.
This object is attained with the device of applying a liquid resin and fine-grained abrasive material, especially corundum onto a continuous paper web for use in the production of abrasion resistant laminates. The device according to the invention is provided with a deflecting roller on which the paper web lies in a looping region, with a metering roller which is arranged parallel to the deflecting roller and includes a narrow gap therewith and is driven synchronously or approximately synchronously with the deflecting roller, with a slit nozzle for applying the coating substance either directly to the paper web lying on the deflecting roller or to the metering roller, and with a doctor blade comprised substantially of a rectangular flap of a flexible rubber like material which is affixed at its rear edge parallel to the axes of the two rollers and which lies slackly on the upper pass departing from the deflecting roller of the paper web.
The uniformity of the applied coating is still further improved by affixing the flap to a support bar which is set into vibration.
The slit nozzle is oriented from above onto the metering roller to allow the coating substance which is applied to the metering roller to be more readily observable. This simplifies the predosing. Since in this arrangement the nozzle slit lies below, the device can be operated with lower pump pressures. The settling of particles in the nozzle is completely avoided.
When the slit nozzle is offser reative to the zenith line of the metering roller in the direction of rotation of the metering roller it is possible to avoid running of the coating substance into the roller gap upon standstill of the machine and smearing of the deflecting roller.